Adaptive braking control system using peak wheel deceleration detector and initial high slip

ABSTRACT

A control portion of an adaptive braking system utilizing peak wheel deceleration to prevent the skidding of an automotive vehicle. The control portion assumes the vehicle is operating on a high coefficient surface for a first cycle of brake pressure modulation. After the first cycle of modulation, if the vehicle is operating on a low coefficient surface, appropriate logic will change the allowable percent slip to a lower value. Along with the initial high coefficient surface condition for the first cycle of brake pressure modulation is included a means to memorize the initial speed upon applying the vehicle brakes. The braked wheel is brought back to a given percentage of the initial speed by further decay of brake pressure during the first cycle of modulation.

atent Hickner et a1.

[ 51 May 22, 1973 54] ADAPTIVE BRAKING CONTROL 3,532,392 10 1970Scharlack ..303 21 P SYSTEM USING PEAK WHEEL 3,532,393 10/1970 Riordan..303/21 BE 3,604,761 9/1971 Okamoto... .303/21 BE X DECELERATIONDETECTOR AND 3,604,762 9/1971 Ando ..303/21 BE INITIAL HIGH SLIP3,578,819 5/1971 Atkins ..303/21 BE [75] Inventors: George B. Hickner;Michael Slavin,

both of South Bend, lnd.; Donald P imary Examiner-Robert J. Spar W.Howard, Baltimore, Md, Attorney-William N. Antonis and Plante, l-lartz,[73] Assignee: The Bendix Corporation, South Smith & Thompson Bend 57ABSTRACT [22] Flled: 1970 A control portion of an adaptive brakingsystem utiliz- [21] A l, N 95,785 ing peak wheel deceleration to preventthe skidding of an automotive vehicle. The control portion assumes thevehicle is operating on a high coefficient surface [52] "303/21 188/181303/20 for a first cycle of brake pressure modulation. After 303/21 Pthe first cycle of modulation, if the vehicle is operating Int. Cl. on alow coefficient Surface pp p logic Fleld of Search B, BE, change theallowable percent to a lower value. 303/21 21 21 21 183/181 A; Alongwith the initial high coefficient surface condi- 324/162 340/262 tionfor the first cycle of brake pressure modulation is included a means tomemorize the initial speed upon [56] References C'ted applying thevehicle brakes. The braked wheel is UNITED STATES PATENTS brought backto a given percentage of the initial speed by further decay of brakepressure during the first 3,656,817 4/1972 Okamoto et a1 ..303/21 P ccle of modulation, 3,525,553 8/1970 Carp et a1. y 3,494,671 2/1970Slavin et al. ..303/20 X 2 Claims, 3 Drawing Figures BRAKE I s FL/PSW/TOLI I R Hop 3 LL i VW V 6;

, SPEED v MEMORY SLIP ADAPTIVE BRAKING CONTROL SYSTEM USING PEAK WHEELDECELERATION DETECTOR AND INITIAL HIGH SLIP BACKGROUND OF THE INVENTIONThe present application incorporates U. S. Pat. Nos. 3,494,671 and3,525,553 which have the same assignee as the present invention.

The above-mentioned patents incorporated by reference should give a gooddescription of the previous controls used in adaptive braking systems.Normally wheel acceleration is determined from the derivative of wheelspeed. The wheel acceleration is then used to modulate the brakepressure to prevent a skidding condition by the automotive vehicle. Inthe previous systems when a predetermined value of wheel decelerationhas been obtained, brake pressure would be decayed as long as wheeldeceleration remains below that value. If wheel acceleration exceeds apredetermined level, then normal braking would be restored to thevehicle operator. Many other set points between these two values couldbe used to give a proportional type of control. If brake pressure isreduced as long as wheel deceleration exceeds the predeterminedreference level, a great deal of braking effort may be lost. Because ofthe time period necessary to restore brake pressure, a better systemwould be one that terminates brake pressure decay at some point in timebefore wheel deceleration has returned to the predetermined referencelevel. Computer studies and test vehicles have proven that peak wheeldeceleration is a very desirable point to terminate pressure decay. Thisresults in increased braking effort with a faster restoration of brakepressure.

Prior systems that use acceleration response type of devices assume thevehicle to be operating on a low coefficient surface. If the vehicle isoperating on a high coefficient surface, then during or after the firstcycle the allowable percent slip is increased. This results in a loss ofbraking effort during the first cycle of operation on high coefficientsurface conditions. Since a far greater percentage of vehicles areoperated on high coefficient surfaces, this results in a significantreduction in the overall braking effectiveness. The present inventionassumes for the first cycle that the vehicle is operating on a highcoefficient surface. If this is incorrect, then on subsequent cycles ofmodulation the percent slip will be reduced which indicates operation ona low coefficient surface. Considering the average surface condition onwhich vehicles are operated, the overall braking effectiveness has beenincreased. If the vehicle is operating on a low coefficient surface, aspeed memory with a percentage comparator has been included to insurethat the vehicle wheel will return to some percentage of its initialvelocity without cycling down to a locked wheel condition.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide a peak wheel deceleration detector to give an earliertermination of brake pressure decay thereby increasing overall brakingeffort.

It is another object of the present invention to utilize an accelerationresponsive device to give an initial slip command that indicatesoperation on a high coefficient surface with a maximum braking effort.

It is still another object of the present invention to change the slipcommand from a high percent slip to a low percent slip after the firstcycle of operation if the vehicle is being operated on a low coefficientsurface.

It is an even further object of the present invention to include a speedmemory and percentage comparator to insure that rotational velocity ofthe vehicle wheel returns to a percentage of its initial wheel velocityupon applying the vehicle brakes thereby preventing premature wheellockup on low coefficient surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a portionof the adaptive braking controls utilizing a peak wheel decelerationdetector in an adaptive braking system.

FIG. 2 is an illustrated schematic showing all the improvements of thepresent invention over the previously incorporated patents.

FIG. 3 is a graphic illustration of how the speed memory shown in FIG. 2extends the brake pressure decay for the first cycle to insure thereturn of the vehicle wheel to a percentage of its initial speed.

DESCRIPTION OF THE PREFERRED EMBODIMENT The essential elements fortermination of brake pressure decay using a peak wheel decelerationdetector are shown in FIG. 1. A wheel speed sensor 10 gives a pulsedoutput signal with the pulses being proportional to the rotationalvelocity of the vehicle wheel (not shown). The counter 12 converts thedigital representation given by the pulses to an analog representationthat is proportional to the rotational velocity V of the vehicle wheel.The rotational velocity voltage output V of counter 12 is fed intoderivative circuit 14 to obtain wheel acceleration represented by A Theacceleration signal A is fed into peak detector 16 that determines thepoint of maximum wheel deceleration. Though not specifically shown inthe drawings for this application, the wheel acceleration signal A feedsinto other logic elements as shown in the incorporated patents. Anoutput from the peak detector 16 feeds into logic gate 18. Logic gate 18controls the operation of air valve 20 used to decay brake pressure.Logic gate 18 receives a number of other inputs with the ones shown inthe incorporated references being a typical example of signals used tooperate the air valve 20. However, once a predetermined signal isreceived from the peak detector 16 (representing maximum wheeldeceleration), the logic gate 18 will close air valve 20 therebypreventing any further decrease in brake pressure.

To explain in further detail the peak wheel deceleration detector 16, asshown in FIG. 1, and other aspects of the present invention, attentionis directed to FIG. 2. A voltage signal proportional to rotationalvelocity of the vehicle wheels, which is the same as rotational velocityin FIG. 1, is again represented by V The rotational velocity V isdetermined by any appropriate means as shown in the prior art or theincorporated patents. A derivative circuit 14 converts the velocitysignal V into an acceleration signal A The acceleration signal A feedsto g;, +g and +g comparators as shown in the incorporated patents. Also,the acceleration signal A feeds into the peak wheel decelerationdetector 16 enclosed by dotted lines. When the acceleration signal Agoes in the negative direction to indicate a wheel deceleration, currentwill flow through diode 22 and resistor 24 to charge capacitor 26. Thecharge on capacitor 26 is connected to the input of an emitter follower29 formed by transistors 28 and 30. The collectors of the emitterfollower 29 are connected to a regulated DC supply represented by +V.The output current of the emitter follower 29 develops a voltage acrossresistor 32 that is essentially equal to the voltage developed acrosscapacitor 26. The time constant for the charging of the capacitor 26 isdetermined by resistor 24 and capacitor 26. Diode 22 prevents dischargeof capacitor 26 in one direction and emitter follower 29 providesisolation for the capacitor 26 in the other direction. The time constantfor discharging capacitor 26 can be set at any desired value. For thepur poses of this invention, the output voltage developed acrossresistor 32 will represent the peak wheel acceleration A The wheelacceleration A is also fed into a filter circuit 34 that removesunwanted noise and, simultaneously, allows the approximate wheelacceleration signal A to be fed into comparator 36. The other input tocomparator 36 is the peak wheel deceleration. When the peak wheeldeceleration exceeds the actual wheel deceleration (A as receivedthrough filter circuit 34, then a voltage output will be generated. Toconvert the voltage output from comparator 36 to the desired form foruse in the incorporated patents, an inverter 38 is necessary. The outputfrom inverter 38 feeds into AND gate 40 which can correspond to AND gate82 or AND gate 95 of U. S. Pat. No. 3,494,671. The other inputs to ANDgate 40, as described in the incorporated patent, would be a brakeswitch BK. SW., +ig', and g slip.

Under normal operation of the vehicle, if an imminent skid condition issensed, a -g slip signal is fed into AND gate 40. Since the brake switchinput BK. SW. and if, are already being fed into AND gate 40 along withthe output from inverter 38, AND gate 40 will give an output thatenergizes solenoid air valve 42. The energization of solenoid air valve42 will result in a decrease in brake pressure as explained inincorporated patent. If the vehicle operator applies enough pressure tocause an imminent skid condition, the first input signal to be removedfrom AND gate 40 would be the signal from inverter 38 of peak wheeldeceleration detector 16. This allows an earlier brake pressure decaytermination which results in increased braking effort due to the finitetime necessary to restore brake pressure.

Also included in the present invention is an initial high slipcontroller 44. The wheel velocity signal V is fed into a voltage divider46 formed by resistors 48 and 50. However, an alternate path as will besubsequently described, may connect resistor 52 in parallel withresistor 50 thereby changing the voltage divider network 46. The slipcommand which is taken from the junction of the voltage dividing network46 is dependent upon mand is reduced, and it is assumed that theautomobile is operating on a low coefficient surface.

The brake switch command feeds into initial high clip controller 44 toset flip-flop 54. When flip-flop 54 is set, the 6 output drops to zerothereby preventing the conduction of transistor 56. With transistor 56being non-conducting, resistor 52 is not connected in parallel withresistor 50. Therefore, a high slip command will be generated. However,once the solenoid air valve 42 has been de-energized, inverter 58 willreset flip-flop 54 to yield a 6 output. Even though the set S and resetR signals for flip-flop 54 may co-exist immediately after the signalfrom the brake switch is received, the leading edge of a signal controlsthe operation of the flip-flop 54 so it will always be set uponreceiving the brake switch command. The 6 output starts conduction oftransistor 56 which connects resistor 52 in parallel with resistor 50 ifthe acceleration responsive switch 60 has not opened. The accelerationresponsive switch 60 may be of a type similar to the one shown in U.S.Pat. No. 3,525,553 which is normally closed when the vehicle is beingbraked on a low coefficient surface and opening only when the vehicle isbeing heavily braked on a high coefficient surface. Therefore, bothacceleration responsive switch 60 must be closed and transistor 56 mustbe conducting before a low slip command will be received.

When operating on a low coefficient surface, it may be possible to lockthe vehicle wheels during the first cycle of operation. To insure that alocked wheel condition does not occur during the first cycle ofoperation, especially on low coefficient surfaces, a percentagecomparator 62 has been included. Within the percentage comparator 62 aspeed memory 64 continuously receives the wheel rotation velocity signalV Upon receiving an enable command which may be the Q output offlip-flop 54 or a direct input from the brake switch, the initialbraking speed V, is memorized. Upon receiving a g slip which indicatesthat an imminent skid condition exists, the inhibit for speed memory 64is removed and an output feeds into voltage divider 66 formed byresistors 68 and.70. The voltage developed at the junction of resistors68 and 70 represents a percentage of the initial rotational velocitysignal V, of the vehicle wheel. The percentage of this initial velocityV, which has been previously set by resistor 68 and 70 is fed intocomparator 72. The other input to comparator 72 is the velocity ofvehicle wheel V The comparator 72 gives an output as long as the actualwheel velocity V is less than the percentage set by the voltage divider66 of the initial velocity V, contained in speed memory 64. The outputfrom comparator 72 feeds into OR gate 74 along with the output of ANDgate 40. Therefore, AND gate 40 may indicate a termination of brakepressure decay by a loss of voltage output, but the output fromcomparator 72 will keep the solenoid air valve 42 in the energizedstate.

A graphic illustration of the operation of the solenoid air valve isshown in FIG. 3. As the wheel speed goes through g slip, the air valve42 is energized. Normally the solenoid air valve would be de-energizedat the point of maximum wheel deceleration 76 but the output fromcomparator 72 maintains the solenoid air valve 42 in the energized stateas shown by the dotted portion 78. It should be emphasized at this pointthat g slip is necessary before a speed memory output can be fed tovoltage divider 66. However, the speed memory output V, is not removeduntil the enable is also removed, even though g slip may no longer ex-As an additional fail-safe feature, speed memory 64 may have a timedelay to remove V, if the enable signal has not been removed, i.e.,flip-flop 54 reset, within a given time period. An example of such acase where no brakes could otherwise result would be where a vehicle hassignificantly reduced its speed between the time the brake switchcommand is received and before a skid condition results, i.e., g slip.Therefore, V would never exceed V, to de-energize solenoid air valve 42which reduces brake pressure without removing V,. The percentagecomparator 62 which receives its enable from flip-flop 54 will only givean output during the first cycle of modulation to maintain the solenoidair valve 42 in the energized state. When flip-flop 54 is set, thecomparator output is at a zero voltage level allowing solenoid air valve42 to be controlled by AND gate 40.

If, in the middle of an adaptive braking cycle, the vehicle moves from ahigh coefficient surface to a low coefficient surface, the change ofstate by the acceleration responsive switch 60 can be used to reset thespeed memory 64 through flip-flop 54. An OR gate at the set S inputwould accept either brake switch BK. SW. or the change of accelerationresponsive switch 60 to set flip-flop 54. Now the initial speed V,contained in speed memory 64 would be the speed where the vehicle movesfrom a high coefficient to a low coefficient surface.

We claim:

1. In a vehicle having a wheel and a brake controlling said wheel, anadaptive braking system for controlling said brake to prevent skiddingof said wheel comprismodulating means responsive to a control signal forrelieving braking pressure communicated to said controlled wheel; and

control means for generating said control signal, said control meansincluding means responsive to acceleration and deceleration of saidvehicle wheel for generating acceleration and deceleration signalsproportional to acceleration and deceleration of said vehicle wheel,means for generating said control signal when said deceleration signalexceeds a predetermined value whereupon said controlled wheel continuesto decelerate to a maximum deceleration level due to the response timeof said adaptive braking system and thereafter said controlled wheelaccelerates, said deceleration signal attaining a peak value when saidcontrolled wheel attains the maximum deceleration level, and meansresponsive to the peak value of said deceleration signal forextinguishing said control signal;

said last-mentioned means including a device for storing theinstantaneous value of said deceleration signal, and means comparing theinstantaneous value of said deceleration signal and generating an outputsignal when the instantaneous value becomes less than the stored value,said output signal being effective to extinguish said control signal.

2. The invention of claim 1:

means for inverting the value of said output signal;

said control means including gating means responsive to a plurality ofinput signals to generate said control signal, said input signalsincluding said inverted value of said output signal and a signalgenerated when the value of said deceleration signal exceeds saidpredetermined value.

1. In a vehicle having a wheel and a brake controlling said wheel, anadaptive braking system for controlling said brake to prevent skiddingof said wheel comprising: modulating means responsive to a controlsignal for relieving braking pressure communicated to said controlledwheel; and control means for generating said control signal, saidcontrol means including means responsive to acceleration anddeceleration of said vehicle wheel for generating acceleration anddeceleration signals proportional to acceleration and deceleration ofsaid vehicle wheel, means for generating said control signal when saiddeceleration signal exceeds a predetermined value whereupon saidcontrolled wheel continues to decelerate to a maximum deceleration leveldue to the response time of said adaptive braking system and thereaftersaid controlled wheel accelerates, said deceleration signal attaining apeak value when said controlled wheel attains the maximum decelerationlevel, and means responsive to the peak value of said decelerationsignal for extinguishing said control signal; said last-mentioned meansincluding a device for storing the instantaneous value of saiddeceleration signal, and means comparing the instantaneous value of saiddeceleration signal and generating an output signal when theinstantaneous value becomes less than the stored value, said outputsignal being effective to extinguish said control signal.
 2. Theinvention of claim 1: means for inverting the value of said outputsignal; said control means including gating means responsive to aplurality of input signals to generate said control signal, said inputsignals including said inverted value of said output signal and a signalgenerated when the value of said deceleration signal exceeds saidpredetermined value.